The Statistical Consulting Service was formally established in 1997 to provide a variety of experimental design and data analysis support to NIEHS research efforts. These activities range from brief consultations on experimental design and data analysis issues to more comprehensive collaborations that result in co-authorship of papers in subject matter journals. Approximately 80 NIEHS scientists, representing a number of different areas of environmental health research, made use of the Statistical Consulting Service this year. The list of publications that accompanies this project report provides more information as to the nature of these research collaborations, which include both laboratory and human studies. Specific examples of collaborative research activities involving the Statistical Consulting Service include an evaluation of reproductive tract carcinogenesis in a multi-generational study of DES, an investigation of the relationships among reproductive endpoints in Swiss mice, using the Reproductive Assessment by Continuous Breeding Database, the evaluation of rodent carcinogenicity in long term studies of 2,2-bis(bromomethyl)-1,3-propanediol, oxazepam, and isobutyraldehyde, and the collaborative development and characterization of the sisterhood design for studying the etiology of breast cancer, based on enrolling a "genetically enriched" cohort of sisters of cases in a prospective cohort design.